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PDBsum entry 4wn0
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Sugar binding protein
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PDB id
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4wn0
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References listed in PDB file
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Key reference
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Title
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Structures of xenopus embryonic epidermal lectin reveal a conserved mechanism of microbial glycan recognition.
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Authors
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K.Wangkanont,
D.A.Wesener,
J.A.Vidani,
L.L.Kiessling,
K.T.Forest.
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Ref.
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J Biol Chem, 2016,
291,
5596-5610.
[DOI no: ]
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PubMed id
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Abstract
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Intelectins (X-type lectins), broadly distributed throughout chordates, have
been implicated in innate immunity. Xenopus laevis embryonic epidermal lectin
(XEEL), an intelectin secreted into environmental water by the X. laevis embryo,
is postulated to function as a defense against microbes. XEEL is homologous (64%
identical) to human intelectin-1 (hIntL-1), which is also implicated in innate
immune defense. We showed previously that hIntL-1 binds microbial glycans
bearing exocyclic vicinal diol groups. It is unknown whether XEEL has the same
ligand specificity. Also unclear is whether XEEL and hIntL-1 have similar
quaternary structures, as XEEL lacks the corresponding cysteine residues in
hIntL-1 that stabilize the disulfide-linked trimer. These observations prompted
us to further characterize XEEL. We found that hIntL-1 and XEEL have similar
structural features. Even without the corresponding intermolecular disulfide
bonds present in hIntL-1, the carbohydrate recognition domain of XEEL (XEELCRD)
forms a stable trimer in solution. The structure of XEELCRD in complex with
d-glycerol-1-phosphate, a residue present in microbe-specific glycans, indicated
that the exocyclic vicinal diol coordinates to a protein-bound calcium ion. This
ligand-binding mode is conserved between XEEL and hIntL-1. The domain
architecture of full-length XEEL is reminiscent of a barbell, with two sets of
three glycan-binding sites oriented in opposite directions. This orientation is
consistent with our observation that XEEL can promote the agglutination of
specific serotypes of Streptococcus pneumoniae. These data support a role for
XEEL in innate immunity, and they highlight structural and functional
conservation of X-type lectins among chordates.
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